What Is an Orifice Flange? Orifice in Piping, Orifice Pipe and Flow Measurement Guide

An orifice flange is a special flange set used to hold an orifice plate in a piping system for flow measurement. Instead of only connecting two pipe ends, the flange pair creates a controlled measuring point where pressure can be taken upstream and downstream of the plate. The pressure difference is then used to calculate flow rate.

If you are asking what is an orifice, the simple answer is: an orifice is a designed opening, hole or restriction through which fluid passes. In industrial piping, the orifice is usually the bore in an orifice plate. The phrase orifice orifice sometimes appears in search data because buyers repeat the word while trying to distinguish a general opening from a piping orifice plate.

What Is an Orifice Flange?

An orifice flange is normally supplied as a pair of flanges with pressure tapping holes machined into the flange body. The orifice plate sits between the two flanges, and the flange pressure taps allow instruments to measure the differential pressure across the plate.

In simple terms, the assembly includes:

• Two orifice flanges, usually weld neck or slip on type.
• An orifice plate with a precisely sized bore.
• Gaskets on both sides of the plate.
• Bolts, nuts and sometimes jack screws for easier separation.
• Pressure taps connected to tubing, valves or a differential pressure transmitter.

Orifice in Piping: How It Measures Flow

An orifice in piping works by creating a known restriction in the flow path. When liquid, gas or steam passes through the orifice plate, velocity increases at the restriction and static pressure changes. By comparing upstream and downstream pressure, the flow rate can be estimated using the selected plate bore, fluid properties and operating conditions.

Part	Function	Why It Matters
Orifice plate	Creates the calibrated restriction	Bore diameter controls the differential pressure signal
孔口法兰	Hold the plate and connect the pipe	Provide a removable, bolted measuring assembly
Pressure taps	Transmit upstream and downstream pressure	Needed for differential pressure measurement
Jack screws	Spread the flange pair during maintenance	Make plate inspection or replacement easier
Gaskets	Seal both sides of the plate	Prevent leakage and preserve measurement accuracy

Orifice Pipe and Meter Run Requirements

The phrase orifice pipe usually refers to the pipe section or meter run where the orifice flange assembly is installed. Flow measurement accuracy depends not only on the flange, but also on pipe straightness, upstream disturbance, downstream recovery and correct installation orientation.

For reliable results, the meter run should avoid placing the orifice flange immediately after elbows, reducers, valves, tees or pumps unless the engineering calculation allows it. Turbulence near the plate can distort the pressure signal. This is why many projects specify a minimum straight pipe length upstream and downstream of the orifice plate.

Common Types of Orifice Flanges

类型	Typical Use	Selection Note
Weld neck orifice flange	High pressure, high temperature or critical service	Good stress transfer through the tapered hub
Slip on orifice flange	Moderate pressure and general industrial service	Often easier to align and more economical
Raised face orifice flange	Standard ASME process piping	Used with compatible soft or semi-metallic gaskets
RTJ orifice flange	High pressure or severe service	Uses a metal ring gasket and machined groove
Custom orifice flange	OEM equipment, retrofit work or special drawings	Requires clear dimensional and material specification

Orifice Flange vs Standard Flange

Standard flanges are mainly used for mechanical connection and sealing. 孔口法兰 are designed for both connection and measurement. The main difference is the presence of pressure taps and the ability to locate an orifice plate accurately between the flange faces.

Item	Standard Pipe Flange	Orifice Flange
Main purpose	Pipe or equipment connection	Flow measurement plus pipe connection
Pressure taps	Not normally included	Machined into flange pair
Plate location	No orifice plate seat required	Designed to hold an orifice plate
维护	General gasket replacement	Plate inspection, bore check and tap cleaning may be needed
标准	Often ASME B16.5, EN, DIN, JIS or project standard	Often ASME B16.36 or project flow measurement specification

What Is a Orifice? Correct Wording for Buyers

Many buyers search what is a orifice, but the grammatically correct phrase is what is an orifice. In technical purchasing, both searches point to the same concept: a designed restriction or opening used to control, meter or direct fluid flow.

The misspelled phrase orfice flange is also common in search logs. It normally means orifice flange. When sending an RFQ, use the correct wording so suppliers can quote the right product, standard and pressure class.

What Is the Orifice Tube?

What is the orifice tube depends on the industry. In automotive air-conditioning, an orifice tube is a small metering device that controls refrigerant flow. In industrial piping, buyers may use the phrase loosely when they mean an orifice plate, restriction or meter run. For a pipe flange order, the correct product name is usually orifice flange assembly or orifice plate assembly, not automotive orifice tube.

Applications of Orifice Flanges

Orifice flanges are used where a simple, robust and widely understood flow measurement point is needed. Common applications include oil and gas pipelines, steam systems, chemical plants, water treatment, compressed air lines, refineries and power generation piping.

行业	Measured Fluid	Why Orifice Flange Is Used
Oil and gas	Gas, crude oil, condensate	Durable measurement point for pipeline and process units
化学加工	Liquids, vapor, utility gases	Works with many materials and pressure classes
发电	Steam, boiler feed water, cooling water	Suitable for engineered meter runs
水处理	Clean water, process water, wastewater	Economical and easy to inspect

Selection Checklist for Orifice Flange Orders

Before ordering an orifice flange, confirm the measurement and mechanical requirements together. A flange can be dimensionally correct but still unsuitable if the plate bore, tap orientation or meter run requirement is wrong.

1. Confirm flange standard, usually ASME B16.36 for many ASME projects.
2. Specify size, pressure class, material grade and face type.
3. Confirm weld neck or slip on design.
4. Define raised face or RTJ facing and matching gasket type.
5. Provide orifice plate bore, plate thickness and material if the plate is included.
6. Confirm pressure tap orientation and instrument connection thread.
7. Check straight pipe requirements upstream and downstream.
8. Request MTC, dimensional report, marking photos and packing details for export.

应避免的常见错误

• Ordering a standard flange when an orifice flange with pressure taps is required.
• Ignoring straight pipe length before and after the orifice plate.
• Mixing raised face and RTJ gasket requirements.
• Choosing material only by price instead of corrosion and temperature service.
• Forgetting jack screws, plug fittings or pressure tap details in the RFQ.
• Using informal words like orifice tube when the project actually needs an orifice flange assembly.

FAQ

What is an orifice flange used for?

It is used to hold an orifice plate in a pipeline and provide pressure taps for differential pressure flow measurement.

Is an orifice flange the same as an orifice plate?

No. The orifice plate is the thin plate with the calibrated opening. The orifice flange pair holds the plate, seals the joint and provides pressure tapping points.

Can orifice flanges be used for gas and liquid?

Yes, they can be used for gas, liquid and steam service when the design, material, pressure class, plate bore and installation conditions are suitable.

Why do orifice flanges have jack screws?

Jack screws help separate the flange faces during maintenance, making it easier to remove or inspect the orifice plate without damaging the gasket surfaces.

Final Thoughts

An orifice flange is more than a pipe connector. It is a flow measurement component that must match the pipe size, pressure class, material, face type, orifice plate and instrument connection. For custom orifice flange orders, Songhai Flange can support standard and engineered flange solutions for oil and gas, chemical, power, water treatment and general industrial piping projects.